<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style type="text/css">
			div{
				border: 1px solid red;
				width: 100px;
				height: 100px;
				/*transition属性，规定元素动作发生时间，
				 属性值以秒为单位，可设定小数值，仅能设定块级元素*/
				transition: 0.5s;
			}
			div:hover{
				width: 200px;
				height: 200px;
			}
		</style>
	</head>
	<body>
		<div></div>
	</body>
</html>